Quote 1
In a single quick movement the boy scrambles to his feet and dodges out of range. "We will kill you all!" he shouts. He turns; deliberately trampling the potato bed, he ducks under the wire fence and retreats toward Petrus's house. His gait is cocky once more, though he still nurses his arm.
Lucy is right. Something is wrong with him, wrong in his head. A violent child in the body of a young man. (23.17-18)
Lucy, David, and even we as readers can see that violence isn't just about actions, but also thoughts. Pollux doesn't just act violently; it seems that he also thinks violently.
Quote 2
The boy does not appear to be startled. On the contrary, the boy appears to have been waiting for this moment, storing himself up for it. The voice that issues from his throat is thick with rage.
"Who are you?" he says, but the words mean something else: by what right are you here? His whole body radiates violence. (15.102)
What makes a bad moment even worse for David is that the person he hates with every fiber of his being is so nonchalant about this confrontation. We feel the hate emanating from every hair on David's head, but of course he's trying not to cause a scene at the party, so he can't do what he really wants to do – kick the living daylights out of the boy.